Semiconductive electromechanical transducers



March 1969 SHlNlCHl SHIBATA ETAL 3,432,732

SEMICONDUCTIVE ELECTROMECHANICAL TRANSDUCERS- Sheet of 2 Filed March 28,1967 FIG. I

E C N M S D SHIN/CH1 SHIBATA M05 MM 19 Man/5m UWADA INVENTORS March 1969SHINICHI SHIBATA ETAL 3,432,732

SEMI CONDUCTIVE ELECTROMECHANICAL TRANSDUCERS Filed March 28, 1967 Sheetg of 2 Ic (mA) 0 o m m O 012 (i4 (i6 0J8 4.'o

W(gr)- United States Patent 3,432,732 SEMICONDUCTIVE ELECTROMECHANI'CALTRANSDUCERS Shinichi Shibata, Tokyo, and Hideo Mori and Atsushi Owada,Yokohama-shi, Japan, assignors to Tokyo Shibaura Electric Co., Ltd.,Kawasaki-shi, Japan, a corporation of Japan Filed Mar. 28, 1967, Ser.No. 626,483 Claims priority, application Japan, Mar. 31, 1966,41/28,587; Apr. 9, 1966, 41/32,148 U.S. Cl. 317235 4 Claims Int. Cl.H011 11/00, 15/00 ABSTRACT OF THE DISCLOSURE A transistor comprises abody of the semiconductive material with a plurality of protrusionsintegrally provided on a top face of said body, said body partitionedinto more than one base region, more than oneemitter region and acollector region, said base and emitter regions extended along at leastexternal surfaces of said protrusions which are respectively flattenedat its top contact face.

A force applicator has a relatively larger flattened face which rests onsaid top con-tact faces for applying a mechanical force to saidtransistor, said transistor converting the transmitted load into currentintensity.

Background of the invention The present invention relates tosemiconductive electromechanical transducers, and more particularly to asemiconductive transducer adapted for converting an alternate load suchas a stylus driving force that is transmitted through a force applicatorto a transistor into current intensity.

A well known semiconductive transducer comprises a planar typetransistor comprising a body of semiconductive material which ispartitioned into a base, an emitter and a collector region by diffusingsuitable impurities on a face of said body, and a needle like forceapplicator made of such a hard material as sapphire, diamond crysstaland which has a tip contact area of the order of microns in curvatureradius, said tip contact area resting on the flat face of thesemiconductive body for applying a mechanical load on the emitter regionof the transistor.

A first problem of those transducers is how to improve the sensitivityof the transducer depending upon variate of the current intensity. Asthe increase of the mechanical load per unit area on the emitter regioncauses the magnitude of collector current to be decreased in suchtransducers for converting the force such as stylus driving force intocurrent intensity, it is desirable that the top contact area is small asfar as possible to enlarge the range of variate of current. An estimatedmaximum load in practice is predestined preferably near but less thanthe value of the elastic limit of semiconductive material so that theload applied on the emitter region is frequently charged, particularlyin the case where said applied load is an alternate load, in excess ofthe elastic limit defined by the fatigue limit of the semiconductivematerial in spite of the fact that the applied load is desirably limitedwithin the elastic limit. Finishing condition of the surface of thetransistor body further causes the transmitted force to be concentratedlocally on said surface. As a result damages such as cracks ordeformations of the contact surface of the transistor are caused by thelocally overcharged force.

It is possible to avoid such damages by utilizing a needle like forceapplicator made of such as tungsten,

iron or the like being softer than diamond or sapphire, but impossible.to avoid degrading the sensitivity of the transducer as the tip of theneedle is deformed by a comparatively lower load which produces aninternal stress in the transistor within the fatigue and locallyallowable limit.

The nearer the loaded area on the emitter region is presented to anemitter junction exposed on the top face of the transistor body, thelarger the variate of current with respect to a certain load applied onthe emitter region is increased. However, as the contact area of theneedle is small, to register the contact area of the needle on theexposed emitter junction is ditficult and as the latter is relativelyweak with respect to the mechanical load, it is undesirable to load theload thereon.

It is necessary to keep the good sensitivity of the semiconductivetransducer and reduce the transmitted load per unit area on the emitterregion.

A semiconductive transducer for deleting these defects is described in acopending application Ser. No. 602,303 filed Dec. 16, 1966, and assignedto the same assignee as the present invention. The transducer asdescribed comprises a transistor which comprises a body of thesemiconductive material with a protrusion integrally provided on a topface of said body, said body partitioned into a base region, an emitterregion and a collector region, said base and emitter regions extendedalong at least external surface of said protrusion which is flattened atits top contact face, and a force applicator having a large flat contactface for face-to-face contact with the contact face of the protrusion.

The exposed emitter junction is positioned out of the contact face sothat when loading a mechanical force or alternate force on the emitterregion at the contact face the exposed emitter junction is kept freefrom destruction due to the mechanical load imposed. Although thedimension of the contact area of the applicator is the same as that ofthe contact face of the protrusion and larger than that of the priorneedle like applicators, an average reduction ratio of current withrespect to the applied load per unit area on the emitter region ismaintained at a level higher than that of the prior art transistor,because of the fact that the nearer to the edge of the contact face orits neighborhood, the greater the variate of the current becomes.

Summary of the invention An object of this invention is to provide asemiconductive transducer comprising a transistor which comprises a bodyof semiconductive material and a plurality of protrusions integrallyprovided on a top face of the body and spaced one from the other, and aforce applicator having a flat contact face which contacts with thecontact faces of said protrusions in face-to-face relationship, wherebythe reduction ratio of current can be maintained with the contact facesof the protrusions.

It has been found that, when the overall contact area between a forceapplicator and a plurality of protrusions equal to the contact areabetween an applicator and a single protrusion as described in acopending application Ser. No. 602,303, an average reduction ratio ofthe current in a transitor having such a plurality of protrusions can bekept at a level higher than that in a transistor having a singleprotrusion. This means that if the same reduction rate is kept, theformer is more advantageous than the latter for keeping further safelythe emitter region against the applied load. Additionally, theapplicator is stably rested on the protrusions and easiness of loading aforce against the applicator under stable condition is improved becausesituations of the protrusions are spaced one from the other.

Description of the drawings FIG. 1 is an observation graph for variateof collector current which is produced in a transistor concerning to theinvention;

FIG. 2 is an elevational view illustrating one embodiment of thesemiconductive transducer according to the invention;

FIG. 3 is a plan view illustrating the embodiment shown in FIG. 2;

FIG. 4 is a sectional view illustrating the embodiment shown in FIG. 2,a force applicator being shown as chain line therein;

FIG. 5 is a sectional view illustrating another embodiment of thesemiconductive transducer, partly broken away, according to theinvention;

FIG. 6 is a sectional view illustrating a further embodiment of thesemiconductive transducer according to the invention; and

FIG. 7 is an indication graph for variate of current with respect to anamount of the applied force on the emitter region.

Detailed of the description Referring to FIGS. 2 to 4, a semiconductivetransducer according to this invention includes a force applicator 24shaped into a circular cylinder and made of such material as sapphire,tungsten, iron or the like, and a transistor comprising a body 15 ofsemiconductive material with three protrusions 12, 13, 14 integrallyprovided on the face of said body 15 and spaced one from the other. Saidprotrusions have flat top contact faces 12a, 13a, 14a for carrying theapplicator. The transistor has a base region 17 extended in the body 15along an area on a top face including external surfaces of theprotrusions, three emitter regions 18, 19, 20 respectively extended inat least the protrusions along its external surfaces, and a collectorregion indicated at 16 by diffusing suitable impurities from side of thetop face of the body.

Portions of emitter junctions 18a, 19a, 20a exposed on a surface of thebody 15 are respectively presented at the base of the protrusions withrespect to each of the emitter regions or may be at the peripherysurface of the protrusions except of the top contact faces.

Except of the external surfaces of the protrusion, there is aninsulating film 23 on the face of the body 15. Mounted on thesemiconductive body 15 through the insulating film is a base electrode22 which is connected to the base region at one end, and mounted on thebottom surface of the body :15 is a collector electrode 21. When theapplicator cylinder 24 is made of such conductive material as iron, itmay be utilized as an emitter electrode.

The applicator 24 of which under surface is flattened and extended atlarge is completely attached and carried on all top surfaces of theprotrusions so that the transmitted force, for example, such alternateload as stylus driving force is suificiently and positively applied tothe emitter regions.

As shown in FIG. 1, variate of current produced in a transistor under atest load is measured in respect of various plots on traverse from amedium portion to a periphery edge portion on the top surface of theprotrusion. The condition of measurement is given for instance by that adiameter of the top contact face of the protrusion is about microns,grounded emitter current gain is hFlE=30, and the depth of the emitterdiffusion is about one micron. In this case, a force applied on theapplicator is 4 gr. It should be comprehended that the absolute variateof current is increased when a load is applied at the periphery edge.

In the arrangement, although the mechanical load per unit area appliedto the emitter regions is decreased by the contact area extended largerthan that of the prior needle like applicator, the reduction ratio ofcurrent as an average value is maintained at a high level so that thegood sensitivity of the transducer is kept and simultaneously it ispossible to avoid such damage as crack or deformation of the surface ofthe transistor.

As the emitter region contacted to the applicator is further separatedinto the three areas corresponding to numbers of the protrusions, rateof whole periphery edge areas of the protrusions against its wholemedium areas are kept larger than those of the case wherein the emitterregion depends on one protrusion so that if the same contact area isconstant, the reduction ratio of the current is further increased or ifthe same reduction ratio of the current is kept, the maximum load perunit on the emitter is reduced because the contact area is extended.

As shown in FIG. 5, a force applicator 124 is coated with gold 12% onthe surface of the body 124a for connecting it to a transistor 116 byalloying the gold to the transistor body made, for instance, of siliconat about 400 C., and particularly to improve conductibility between theforce applicator and the emitter regions in the case where the forceapplicator is utilized as emitter electrode. As a result, it is possibleto cause the best contact condition to be effected between theapplicator and the top contact faces of the protrusions without theeffect according to the finishing of the face. Alternatively, theapplicator 124 may be connected to the transistor 116 by conductingbonding material.

Referring to FIG. 6, a transistor comprises a body with a stage 200integrally provided on its face, and therewith three protrusions 212,213 and 214 integrally provided on its face. Said body is partitionedinto a base region 217 extended in a top face along an area includingthe external surface of the stage, three emitter regions 218, 219 and220 extended in a top face along areas including at least the externalsurfaces of the protrusions, and a collector region which is remains. Abase electrode is indicated 222 and a collector electrode is indicatedat 221. A force applicator cylinder 224 rests on the protrusions.

In these embodiments, it is advantageous that said protrusions carryingthe applicator are disposed on one face of the body away from each otherfor placing the applicator on the transistor as described in themeantime.

FIG. 7 indicates an observated finding of one embodiment according tothe invention, wherein variate of current produced in transistor isvaried in respect of transmitted force value (gr) against thetransistor.

Although in the foregoing embodiments the transducer of this inventionhas been described and illustrated as having three protrusions, a pluralnumber of such protrusions may be provided. In the embodiments, thenumber of the emitter regions is proportioned to that of theprotrusions, but may be common to a plurality of the protrusions and thebase region is common to a plurality of the emitter regions, but may beproportioned to the number of the emitter region.

Alloying the gold to the transistor body may be changed by alloying suchmetal that is melted at suitable low temperature limited not to invadecharacter of the transistor.

While the invention has been described in connection with someembodiments it will be obvious to those skilled in the art that theinvention is not limited to the preceding examples but various changesand modifications can be made in the details of structure withoutdeparting from the true spirit and scope of the invention.

What is claimed is:

1. A semiconductive electromechanical transducer comprising a transistorwhich comprises a body of the semiconductive material and a plurality ofprotrusions integrally provided on a top face of said body, said bodypartitioned into more than one base region, more than one emitter regionand a collector region by diffusing suitable impurities on said face ofthe body, said base and emitter regions extended along at least externalsurfaces of said protrusions, said protrusions respectively flattened atits top contact face, and a force applicator having a large flat facewhich rest on said top contact faces for face-to-face contact with thetop contact faces of the protrusions.

2. A semiconductive electromechanical transducer according to claim 1 inwhich the applicator is made of conductive material and serves as anemitter electrode.

3. A semiconductive electromechanical transducer according to claim 1 inwhich the transistor has on said body a stage having the protrusionsthereon, the base region being extended on an area including an externalsurface of the stage.

4. A semiconductive electromechanical transducer according to claim 1 inwhich the applicator is alloyed on the protrusions of the transistor bymetal melted at suitable low temperature which is limited not to invadecharacter of the transistor.

6 References Cited UNITED STATES PATENTS 2,837,704 6/1958 Emeis 3l72352,929,006 3/1960 Herlet 317--235 5 3,194,699 7/1965 White 148-4863,244,555 4/1966 Adam et al. 117212 3,292,057 12/1966 Touchy 317--2343,319,068 5/1967 Beale et a1. 250-217 3,398,335 8/1968 Dill 317-235 103,372,244 3/1968 Sikorski 179-110 JOHN W. HUCKERT, Primary Examiner.

I. R. SH EWMAKER, Assistant Examiner.

